The present invention relates to a technique for detecting a crank angle corresponding to a maximum internal cylinder pressure for each cylinder having an pressure sensor.
In order to carry out a feedback control of ignition timing toward a predetermined desired crank angle, an internal cylinder pressure sensor is provided in each cylinder for detecting a maximum internal cylinder pressure so as to determine a crank angle when the maximum pressure is detected. In this technique, when a control for suppressing an engine output is performed, for example, when ignition timing is retarded for a rapid warming-up of catalyst after the engine starts, the ignition is made around the top dead center (TDC) or after the top dead center and the pressure generated by combustion is relatively low. As a result, it is possible that a pressure at the top dead center of a piston is determined to be the maximum pressure.
Japan Patent Application Publication No. S63-78036 proposes a technique for avoiding a wrong detection of a pressure at a top dead center as the maximum pressure during an ignition timing retard operation. This publication discloses an engine combustion detecting apparatus for detecting an engine combustion pressure so as to determine a combustion state based on the maximum value of the detected combustion pressures. Specifically, the disclosed apparatus includes a combustion detecting unit for determining the combustion state by presuming the pressure at a predetermined crank angle after the top dead center of a piston to be the maximum pressure when the maximum pressure sensed during a combustion cycle in a cylinder is equal to the pressure at the top dead center.
The above-referenced technique is intended to determine the combustion state by presuming the pressure at a predetermined crank angle after the top dead center of a piston to be the maximum pressure when the maximum pressure sensed during a combustion cycle in a cylinder is equal to the pressure at the top dead center. However, that approach does not detect a crank angle (θPmax) corresponding to a maximum combustion pressure based on an actual combustion pressure waveform.
As for a multi-cylinder engine, in order to control combustion in each cylinder, it is required to detect a θPmax in each cylinder. It is an objective of the present invention to meet such a requirement.